The present invention relates to a drill chuck. More particularly this invention concerns a multiple-jaw chuck used on a power drill.
A standard drill chuck has a chuck body adapted to be rotated by a power unit about an axis and formed with a plurality of angularly equispaced and angled guides. Jaws in the guides have outer edges formed with teeth meshing with an internal screwthread of a tightening ring axially fixed but rotatable on the chuck body. Typically the ring is formed as a two-part machined casting that is held together by an annularly continuous tightening sleeve slipped axially over it and fixed to it. Rotation of the ring and sleeve in one direction moves the jaws axially forward and radially together, and opposite rotation moves them back and apart.
Typically the tightening ring is set in a radially outwardly open groove of the chuck body with axially forwardly and axially rearwardly directed faces of the groove confronting the ends of the ring. The ring bears axially backward via a roller bearing.
When the jaws move axially backward they reach an end position in which the ring engages an unthreaded portion of the jaws and can no longer rotate. It is, unfortunately, fairly common for the tool operator to dechuck a tool by solidly gripping the sleeve to arrest it and then reverse rotating the chuck body by means of the power unit of the drill, so that the rear-end position is reached rapidly and the ring and jaws jam together.
Even if it is possible to unjam the chuck once this happens, with time this style of operation leads to damage to the threads of the tightening ring. The chuck becomes loose and sloppy.
It has been suggested to provide a spring washer between rear faces of the jaws and the tightening ring. This is a partial solution which avoids some damage to the jaws and ring, but that still can let the chuck jam when moved very rapidly into the fully open position. Even with this system, it is the jamming of the tightening-ring screwthread and the jaw teeth that stop opening action, and this jamming is certain to wear down these parts with time.
It in therefore an object of the present invention to provide an improved drill chuck.
Another object is the provision of such an improved drill chuck which overcomes the above-given disadvantages, that is which does not jam or damage itself if its jaws are moved brusquely into the rear-end position.
A chuck has according to the invention a chuck body rotatable about an axis and formed with a plurality of angularly spaced and forwardly open angled guides holding respective jaws each having a toothed edge and an axially rearwardly directed face. A tightening ring rotatable about the axis on the chuck body is axially relatively nondisplaceable on the chuck body and has a screwthread meshing with the toothed edges of the jaws so that rotation of the ring in one direction moves the jaws axially forward and radially together and opposite rotation moves the jaws axially rearward and radially apart. A spring washer is rotatable about the axis on the body between the tightening ring and the rear jaw faces. The jaw faces are axially rearwardly engageable with the washer to press same toward the tightening ring and coupling formations on the washer and an the ring prevent relative rotation of the washer and the ring when the washer is pressed axially rearward by the faces against the ring. Stop formations on the washer are engageable with the jaws for permitting only limited relative angular movement of the washer and jaws when the faces are pressed axially rearward against the washer.
The spring washer therefore does basically nothing when the jaws are not at or near their fully retracted positions, because the jaw faces are normally out of contact with the spring washer. In fact the spring washer normally is free to rotate about the chuck body. When, however, the jaws are retracted sufficiently to press the spring washer against the tightening ring, this action first locks the spring washer to the tightening ring, and then prevents further relative rotation of the jaws, which are rotational with the chuck body, and the spring washer, which is rotational with the tightening ring that itself is fixed to the standard external tightening sleeve. Thus instead of the jaws bottoming out in the threads of the tightening ring to end relative rotation between the tightening ring and the chuck body, the spring washer engages between the jaws and the tightening ring. This not only protects the somewhat more delicate structure of the jaw teeth and tightening-ring screwthread, but also puts between the jaws and the tightening ring a spring element that is unlikely to bind or jam. Subsequent advance of the jaws is easy as the spring washer in fact will exert a spring force in the appropriate direction. The spring washer angularly couples the chuck body to the tightening ring before the jaws move so far back that the jaw teeth bottom in the tightening-ring screw-thread, so that this structure is not damaged and, when the chuck is to be tightened, the screwthread and jaw teeth are not jammed together.
The coupling formations according to the invention include an axially projecting bump and an axially open seat in which the bump is receivable. More particularly, the bump is formed on the spring washer and the seat on the tightening ring. In fact the spring washer is formed with a plurality of the stop bumps and the ring is formed with a complementary plurality of the seats.
The stop formations according to the invention similarly include at least one axially forwardly projecting bump formed on the washer and angularly engageable with at least one of the jaws. More particularly the jaws are angularly equispaced and for each of the jaws there is a respective one of the stop bumps which themselves are angularly equispaced. Thus all of the jaws will bear angularly via the respective stop bumps on the spring washer which will in turn bear angularly via the coupling bumps on the tightening ring.
According to the invention a spring ring bears axially rearwardly on a shoulder of the chuck body that engages at most over half of the washer""s radial dimension. The tightening ring bears in turn radially backward on the spring ring at a location radially outward of the shoulder 80 that the spring ring can be deformed elastically by axial rearward pressure of the tightening ring on the spring ring. In practice it has been found advantageous when the shoulder engages over only about one-quarter of the radial dimension of the spring ring, to maximize the extent to which the outer periphery of the spring ring can be elastically deformed and thereby maximize the spring effect. In any case bearing balls engage axially between the tightening ring and the spring ring, and the spring ring has a front face formed as a track for the balls.